Gun system comprising an ion trap



Jan. 12, 1960 w. BERTHOLD GUN SYSTEM COMPRISING AN ION TRAP Filed March 22, 1956 INVENTOR. Vl 55875 04 0 n m m T 4 -States GUN SYSTEM coMrmsmo AN ION TRAP Wolfgang Berthold, Stuttgart-Wei] im Dorf, Germany, as-

signor to International Standard Electric Corporation, New York, N.Y., a corporation of Delaware The object of the hitherto conventional beam generating or gun systems employing an ion trap is to prevent negative ions, which are produced in the close proximity of the cathode, from reaching the fluorescent screen of the cathode ray tube. It has been proved, however, that aren't 1 in addition negative ions can also be produced in the vi- .cinityof the cathode when positive ions hit the matter with a predetermined speed. The positive ions are produced inthe cathode ray by the impact between electrons and neutral gas molecules. Due to the accelerating field between cathode and anode the positive ions are accelrated in direction toward the cathode and are deflected towards the side on account of the electric field of the ion .trap and strike the electrode that is negative compared with the anode, such as control grid, screen grid and sharpness or focusing electrode.

For a gun system comprising an ion trap in which, due to a combination of electric fields with magnetic fields, there is caused a separation of negative ions and electrons which are produced in the close proximity of the cathode,

it is proposed in accordance with the invention that the negative ions, released by the positive ions, produced in the electronbeam when hitting an electrode which is negative in relation tothe anode, are substantially provided with a strong sideway initial speed by a potential, or are trapped by means of a diaphragm arranged between the anode and the impinged electrode.

The negative ions are given a'sideway initial direction 'byan, inclined portion of the electrode onto which the positive ions impinge. The potential lines between the cathode and the anode adapt themselves to this electrode is possible that the negative ions, which are released by the positive ions, are kept away from the screen by means of a diaphragm arranged in front of the electrode to be impinged. The diaphragm may be embodied by an electrode which is necessary for the focusing of the electron beam, in that this electrode is either provided with a special aperture for the passage of the positive ions, or the aperture serving to focus the electron beam is designed in such a way that the positive ions may impinge on the next successive electrode, but that the majority of the released negative ions are trapped by the described electrode.

In the following the invention will be particularly described with reference to the exemplified embodiments as shown in Figs. l to 3 of the accompanying drawing.

In Fig. 1 there is shown a gun system, the particular shape of which is not to be considered as a limitation to the invention. Reference numeral 1 denotes the neck of a cathode ray tube, 2 the cathode, 3 the control electrode, 4 the screen grid, 5 the anode cylinder, 6 a focusing electrode and 7 the second anode cylinder. The asymmetrical diaphragm 8 in anode cylinder 5 produces the electric r' 2,921,212 Patented -Jan.12, 1

field that deflects the negative ions from the cathode away from the axis and lets them impinge on the diaphragm 9. The magnet 10 returns the electrons to the axis and directs them through the aperture of the diaphragm 9 to the fluorescent screen.

At the point 11, the screen grid 4 is provided with an aperture through which pass the majority of the positive ions without producing the detrimental negative ions. In the case of tubes with an asymmetrical anode diaphragm the point of impingement of the positive ions is about Mt D away from the center axis of the tube (D= of the electron lens with respect to screen grid and anode). Hence the aperture in the screen grid must be arranged about M1 D away from the axis in the same direction as the center point of the asymmetrical diaphragm.

It is also possible to combine the aperture provided for the passage of the electrons with the one provided for the positive ions. In such a case the axial-symmetrical aperture must be big enough for the positive ions to impinge on the electrode arranged behind it, but such that the majority of the released negative ions are trapped by the electrode. The nontrapped negative ions have such a high sideway speed that they are unable to reach the fluorescent screen.

One example of embodiment of such an electrode arrangement is shown in Fig. 2 of the drawings, in which electrode 4 of Fig. l is replaced by the electrodes 12 and 13, which are either on the same or on a diflerent potential. The positive ions hit the electrode 12, and the negative ions, which are released thereby, are trapped for the greatest part by the electrode 13.

Another exam le of embodiment of the invention is shown in Fig. 3 of the drawings. Instead of being provided with an aperture or consisting of two spaced electrodes, the electrode 4 of Fig. 1 is axial-symmetrically inclined at the point 14. By means of this inclination of the electrode the negative ions, which are released by the positive ions, are provided with a sideway initial direction and can no longer reach the fluorescent screen. This embodiment bears the advantage that besides the inclination, chamfer or taper of the electrode there are required no further arrangements. This shaping may be carried out when manufacturing the electrode.

What is claimed is:

1. In an electron gun system for producing a beam of electrons and comprising a plurality of electrodes, including an anode electrode, a cathode electrode, and a further electrode which is at a negative potential with respect to said anode electrode, said electrons being accompanied by negative ions and producing positive ions in said beam which travel toward said cathode electrode, and further comprising ion trap means which separates said negative ions from said electrons and which deflects said positive ions outwardly of said beam, negative ion suppressing means, including said further electrode, for preventing further negative ions produced outside of said beam by said positive ions striking an electrode of said system from following the path of said beam to the terminal end thereof, said further electrode having an aperture therein permitting the passage of said outwardly deflected positive ions through said aperture and said suppressing means comprising a portion of one of said electrodes disposed outwardly of said beam and disposed with respect to the positive ions passing through said aperture and with respect to said further electrode to cause further negative ions produced by positive ions striking said portion to follow paths terminating at one of said electrodes.

2. An electron gun system according to claim 1 wherein said further electrode is intermediate said ion trap means and said cathode electrode and has a second aperture therein displaced from the first-mentioned aperture thereiniafld said further electrodeis mountedwitli said second aperture in alignment with said beam to permitpassage of said beam therethrough.

3. An electron gun system according to claim 1 wherein said: further. electrode is intermediate; said ion trap means and said cathode electrode and said. aperture, in; said further electrode is aligned-with said beam and;is larger thanthe cross-section of said beam toipermit passage, of both said beam and said outwardly deflected; positive ions therethrough and is surrounded by a portionof said further electrode extending outwardlyzfrom, said beam and wherein said first-mentioned one. electrode; is: disposed intermediate said further electrodeand saidrcathode.,electrode, said portion of said one electrodejbeing spaced from, said portion of: said,- further. electrode: and, being mounted in the path of said positive ions passingthrough said aperture and extending adjacent said; portion ofisaid further electrode, said paths of:saidfurthernegativeions terminating at said last-mentionedportion,

, 4. An electron gun system-according-t0,claim,,3;wherein said portion of said further electrode-is a centrally aperturedplate extending transversely tosaid beam; and said first-mentioned one electrode is a further.- centrally. apertured plate spaced from said plateof said further electrode and substantially parallel thereto, the aperture in said further platebeing aligned with the; apertureinsaid'firstmentioned plate.

5. An electron gun system according to claim 1, wherein said further electrode is intermediate saidiontrapmeans and said cathode electrode, the end of said-further-electrode nearer said cathode electrode comprising an end plate with a central aperture therein, forming said one portion, said further; electrode beingrnounted with said end plateaperture in alignment with the axis of said beam to permit passage of said beam therethrough; and said end plate having an axially-symmetrical tapering contour, said first-mentioned aperture'beingin the end1of said; further electrode nearer said ion trap-means.

6. An electron gun systemwaccording to clainr.Sgwherein said end plate has the contour of a hollow, truncatedcone.

7. An electron gun system for producing an electric beam having a given directionandincluding electrons and positive and negative ions, said system comprising cathode, control, screen and anode electrodes arranged in the order named, said control, screen and anode electrodes each having an aperture therein aligned'with the path of said beam to permit the passage of;said beam through the apertures, and ion trap means disposed on the side of said screen electrode remote from -said cathode electrode for separating the ,negativeions from the electrons in said beam, said ion trap means causing outward deflection of said positive ions from said beam toward said screen electrode and said screen electrodehavinga second aperture therein displaced outwardly from the path of said beam and from the aperture-therein permitting the passage of said beam, said second aperture being disposed in the path of said'outwardly defiectcdpositive ions andpermitting. the passage of,saidpositiveionstherethrough.

8. An electron gun system for producing an electric beam having a given direction and including electrons and positive and negative ions, said system comprising cathode, control, positive ion intercepting, screen and anode electrodes arranged in, the order named, saidcontrol, intercepting screen and anode electrodes each having an aperture therein aligned;with,the-pathof said beam: to permit the passage of saidbeamthroughthe apertures, and: ion

trap means disposed onthe side of saidscreen electrode,

remote from said cathode. electrode for separating the negative ions from the electrons in said'beam, said ion trap means causing outwardadeflection of said positive 7 ions from said beam toward a portion of said intercepting electrode outside of said beam and spaced from said screen electrode in the direction of said cathode electrode and the aperture in said screen electrode being larger than the cross-section than said; beam andpermitting the passage of-said outwardly deflected positive ions therethrough and to saidportionof said intercepting electrode, said screen electrode having a portion extending transversely to the path ofsaidbeam and spacedfrom said beam-a distancesubstantiallyequal to the'spacing of said portion of said'intercepting electrode-from said beam for trapping negative ions produced by the striking of said positive ions against said portion of saidintercepting electrode. i

9'. An electron gun system for producing anelectric beam having a givendirectionandiricludingelectrons and positive and negative ions, said system-comprising cathode, control, screen and anode electrodes arranged'in the order named, said control, screen and anode electrodes each having an aperture thereinaligned with the pathof said beam to permit the passage of 'said beam through the apertures, and'ion trapmea'ns disposed on-the'side' of said screen electrode remote from said cathode electrode for separating the negativeions from the electronsin said beam, said ion trap means causing outwarddeflection of said positive ions from said. bearntoward said screen electrode and said screen electrode having a portion extending symmetrically around the path'of'said beam and aroundthe aperture. therein permitting the-passage of said beam, the side of said portion nearer said anode electrode, in a section taken substantially parallel to the path of said beam, sloping toward said anode-electrode from-adjacent saiclllpath to the periphery thereof more remote-from said pat ReferencesCitedjn the-fileof this patent, UNITED STATES PATENTS 

